Rome\'s 3 biggest mistakes.

[Robert Vermaat]

If they had taken Germania, they would have had a shorter border to defend as pointed out.
And of course it was the over taxation by the Religious elite that helped
increase the burden on the common people. This carried on into the middle ages.......

Sorry, but that would not have added very much to the problem, which really had its root in the enormous differences between the upper class and the lower class. The gap between the super rich who were also exempt from paying many taxes and other civilian duties and the middle and lower classes was enormous.

For me, this problem ranks as number 2. It created a lack of loyalty towards the Roman state which eventually cause civilians to side with Goths and Feranks in Gaul, or with Arabs in Africa.

Problem number 1 for me is the inability for the Roman emperors to create a secure stable succession system.

Problem 3 would be the inability to create a military system that would have discouraged generals to try taking controle of (parts of) the empire. Civil wars did far more damage than foreign invasions.

1- succession
2- society
3- military